A robust polymerization technique that enables the surfactant-free aqueous synthesis of a high solid content latex containing polymeric hollow particles is presented. Uniquely designed amphiphilic macro-reversible addition fragmentation chain transfer (RAFT) copolymers were used as sole stabilizers for monomer emulsification as well as for free-radical emulsion polymerization. The polymerization was found to be under RAFT control, generating various morphologies from spherical particles, wormlike structures to polymer vesicles. The final particles were dominantly polymeric vesicles which had a substantially uniform and continuous polymer layer around a single aqueous filled void. They produced hollow particles once dried and were successfully used as opacifiers to impart opacity into polymer paint films. This method is simple, can be performed in a controllable and reproducible manner, and may be performed using diverse procedures.

Recent advances in the use of reversible addition–fragmentation chain transfer (RAFT) polymerization in dispersed phase systems have paved the way for the fine control of the morphology of latex particles that was not possible by conventional free radical polymerization techniques. With this approach, living amphiphilic block copolymers are synthesized that self-assemble to form micelles. The hydrophilic segment is formed from a water-soluble monomer which stabilizes the latex particles as polymerization proceeds and the latex particles grow. The hydrophobic ends of the RAFT diblocks ultimately grow into the polymer that forms the body of the particles. This paper presents examples of ways in which these advances can be used to engineer latex particles with unique morphologies that exhibit specific application properties.

Amphiphilic, RAFT-capped, (acrylic acid)x(styrene)y diblock copolymers (x ≅ 10, y = 10, 5, 0) were synthesized and used as stabilizers in emulsion polymerization. Above the critical micelle concentration (cmc) of the diblocks and under appropriate reaction conditions micelles of the more hydrophobic diblocks were sufficiently nonlabile to be nucleated and act as seed particles for latex particle formation. The key parameters which allow control over the system are diblock hydrophobicity and initiator concentration. A homogeneous nucleation mechanism is most likely to operate below the cmc of the diblocks.

Controlled radical polymerization using RAFT has the potential to make polymers with virtually any desired molecular architecture. For this to be implemented on an industrial scale, it must be performed by polymerization in disperse media. However, simply adding a RAFT agent to a conventional emulsion polymerization recipe leads to a loss of molecular weight control and formation of coagulum, probably because of nucleation in droplets, which is normally an unlikely phenomenon in emulsion polymerizations. Recently, a method has been devised for implementing RAFT in ab initio emulsion polymerization that avoids droplets in the particle formation stage. The molecular weight distribution of the polymer thus formed shows that molecular weight control is maintained throughout the polymerization. A model is developed to predict the particle size formed in this new type of emulsion polymerization. The new methodology enables synthesis of novel dispersions where molecular architecture can be precisely controlled, such as structured core-shell particles.

A method is developed to enable emulsion polymerization to be performed under RAFT control to give living character without the problems that often affect such systems: formation of an oily layer, loss of colloidal stability, or loss of molecular weight control. Trithiocarbonate RAFT agents are used to form short stabilizing blocks from a water-soluble monomer, from which diblocks can be created by the subsequent polymerization of a hydrophobic monomer. These diblocks are designed to self-assemble to form micelles. Polymerization is initially performed under conditions that avoid the presence of monomer droplets during the particle formation stage and until the hydrophobic ends of the diblocks have become sufficiently long to prevent them from desorbing from the newly formed particles. Polymerization is then continued at any desired feed rate and composition of monomer. The polymer forming in the reaction remains under RAFT control throughout the polymerization; molecular weight polydispersities are generally low. The number of RAFT-ended chains within a particle is much larger than the aggregation number at which the original micelles would have self-assembled, implying that in the early stages of the polymerization, there is aggregation of the micelles and/or migration of the diblocks. The latexes resulting from this approach are stabilized by anchored blocks of the hydrophilic monomer, e.g., acrylic acid, with no labile surfactant present. Sequential polymerization of two hydrophobic monomers gives completely novel core-shell particles where most chains extend from the core of the particles through the shell layer to the surface.

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (Cn−2H2n−3CHCH2O(CH2CH2O)mH)2(CH2)6 (or GemnEm), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n=12, 14, and 20 and m=5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100°C. Surfactants with small m (i.e., n=12, 14, m=5 and n=20, m=10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10−7 to 10−6 M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.

ADVERTISEMENT RETURN TO ISSUECommunication to the...Communication to the EditorNEXTMiniemulsion Polymerization Stabilized by Amphipathic Macro RAFT AgentsBinh T. T. Pham, Duc Nguyen, Christopher J. Ferguson, Brian S. Hawkett, Algirdas K. Serelis, and Christopher H. SuchView Author Information Key Centre for Polymer Colloids, Chemistry School F11, University of Sydney, NSW 2006, Australia, and Dulux Australia, McNaughton Road, Clayton, VIC 3168, Australia Cite this: Macromolecules 2003, 36, 24, 8907–8909Publication Date (Web):October 30, 2003Publication History Received10 August 2003Revised9 October 2003Published online30 October 2003Published inissue 1 December 2003https://pubs.acs.org/doi/10.1021/ma035175ihttps://doi.org/10.1021/ma035175irapid-communicationACS PublicationsCopyright © 2003 American Chemical SocietyRequest reuse permissionsArticle Views1510Altmetric-Citations100LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Emulsions,Monomers,Polymer particles,Polymers,RAFT polymerization Get e-Alerts

ADVERTISEMENT RETURN TO ISSUECommunication to the...Communication to the EditorNEXTEffective ab Initio Emulsion Polymerization under RAFT ControlChristopher J. Ferguson, Robert J. Hughes, Binh T. T. Pham, Brian S. Hawkett, Robert G. Gilbert, Algirdas K. Serelis, and Christopher H. SuchView Author Information Key Centre for Polymer Colloids, Chemistry School F11, University of Sydney, NSW 2006, Australia, and Dulux Australia, McNaughton Road, Clayton, Vic. 3168, Australia Cite this: Macromolecules 2002, 35, 25, 9243–9245Publication Date (Web):November 8, 2002Publication History Received16 August 2002Revised18 October 2002Published online8 November 2002Published inissue 3 December 2002https://pubs.acs.org/doi/10.1021/ma025626jhttps://doi.org/10.1021/ma025626jrapid-communicationACS PublicationsCopyright © 2002 American Chemical SocietyRequest reuse permissionsArticle Views5201Altmetric-Citations390LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Animal feed,Monomers,Polymers,Radical polymerization,RAFT polymerization Get e-Alerts

The effects of composition on the glass transition of dry and hydroplasticised copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and 2-hydroxypropyl methacrylate (HPMA) were studied by differential scanning calorimetry. Results from the hydroplasticisation studies showed that a high PHPMA content (>75 wt.%) was required for high water absorption and that the amount of water uptake was not linear with HPMA content but increased in an accelerating manner with increasing HPMA content. This behaviour was attributed to the increase in the hydrophilic character of the copolymer due to the strong hydroxyl–hydroxyl interactions at high PHPMA content. The Tgs of the dry copolymers were successfully predicted by all three equations used (rule of mixtures, Fox and Gordon–Taylor) but were poorly predicted for the hydroplasticised copolymers. This failure was attributed to the inadequacy of the equations in accounting for the specific interactions between the different segments of the copolymer chains. HPMA depressed the Tg of the water-saturated copolymers but enhanced the Tg of the dry system and this behaviour has particular relevance to its use in water-based latex paints.

The curing mechanisms and kinetics of diglycidyl ether of bisphenol A using 1-methylimidazole (1-MI), 2-methylimidazole (2-MI), 2-phenylimidazole (2-PhI) and 1,2-dimethylimidazole (1,2-DMI) as the curing agents were studied using scanning and isothermal differential scanning calorimetry (DSC). Both scanning and isothermal DSC studies indicated that only 1-MI was an effective curing agent, resulting in a high degree of conversion and high T-g, at relatively low concentrations. In the scanning DSC studies, multiple peaks were observed for the 2-MI and 2-PhI curing systems whereas only a single peak was observed for the 1-MI curing system. These peaks were assigned to adduct formation, etherification (via the alkoxide anion) and to the process of imidazole regeneration. In the isothermal DSC studies, two peaks were observed for all curing systems being attributed to adduct formation and etherification. The differences in curing behaviour of the three imidazole curing agents was discussed in terms of steric versus inductive effects caused by the substituent attached to the imidazole ring located at the 2-position, and of differences in their initiation mechanism.The curing mechanisms and kinetics of the 1-MI curing system was also investigated in the presence of a salt, tetramethylammonium chloride, hydrochloric acid and water, and were discussed in terms of their effects on adduct formation and on the stability of the propagating alkoxide anion. (C) 2000 Elsevier Science Ltd. All rights reserved.